Regarding conventional semiconductor element cooling structures, for example, Japanese Patent Laying-Open No. 2006-295178 discloses a heat sink device for an electronic element directed to maintaining a uniform flow rate of a heat absorbing fluid such that a surface in contact with the electronic element has a constant temperature (Patent Document 1).
The heat sink device disclosed in Patent Document 1 has a plurality of flow passages partitioned at predetermined intervals by a plurality of flow passage walls, and an inflow guide portion guiding the heat absorbing fluid flowing in through an inflow port to each of the plurality of flow passages. The inflow guide portion is provided with an inflow guide plate which is linearly inclined such that its flow passage cross sectional area decreases with distance from the inflow port. Further, in another heat sink device, one ends of the plurality of flow passage walls are formed to extend longer toward the inflow guide portion with distance from the inflow port such that the flow passage cross sectional area of the inflow guide portion decreases with distance from the inflow port.
In addition, Japanese Patent Laying-Open No. 2003-33002 discloses a power conversion device directed to being able to prevent thermal interference of another heat sink and increasing the number of semiconductor elements without increasing the area of a portion facing a cooling gas (Patent Document 2). In the power conversion device disclosed in Patent Document 2, a plurality of radiating fins are attached to a heat receiving plate to constitute a heat sink. The radiating fins of the heat sink on a side close to an inlet for the cooling gas are formed in a stair-like manner such that they protrude more with distance from the inlet.